In photo detector array fabrication, it is sometimes necessary to have devices which are thinned from the backside due to operational requirements. These requirements may include but are not limited to; maximizing UV spectral response; minimizing sensitive volume thickness; and antiblooming considerations. Difficulties arise in mechanically or chemically thinning or removing the substrate, if the devices are physically small, or the feature size of the device is small, or the doped layers are very thin. Mechanically stressing the device should be minimized. In addition, thinning the substrate may effectively remove the ground path from the device, depending on design. Accuracy in thinning is necessary to achieve uniformity of response.
Previous techniques within the prior art for backside thinning of image sensors have been disclosed such as the chemi-mechanical illustrated in U.S. Pat. No. 5,162,251 issued to Poole et al. (hereinafter referred to as Poole). Other prior art techniques have disclosed chemical etching techniques for backside thinning such as U.S. Pat. No. 5,244,817 issued to Hawkins et al. (hereinafter referred to as Hawkins). Neither of these teachings provide the ability to thin substrates in both a timely and accurate manner.
As can be seen from the foregoing discussion, there remains a need within the art for a method and apparatus that can effectively thin semiconductor image sensor substrates highly accurately and in a timely manner.